1. Field of the Invention
The present invention relates to a lithography photo mask for use in manufacturing a semiconductor device.
2. Description of Related Art
With high integration of the semiconductor integrated circuit in recent years, a pattern size also become fine, alignment accuracies between the pattern and a base become an issue in lithography. Therefore, numerous studies have been made as regards a technique for improving the alignment accuracy.
Among them, thermal expansion in an exposure process of a photo mask (a reticle) is one of factors for deteriorating the alignment accuracy. More specifically, the photo mask (the reticle) comprises a mask substrate (a reticle substrate) composed of a transparent substrate, and a dark film (a dark portion) which is provided on the mask substrate (the reticle substrate) and which has either a function for shielding light or a function for passing through the light partially. Absorption energy from a radiation beam during exposure heats the photo mask (the reticle) to make the photo mask (the reticle) expand. Under the circumstances, when there is any bias in distribution of an arrangement of the dark film (the dark portion) on the mask substrate (the reticle substrate), bias occurs in absorption heating value, and then the accuracy of the alignment accuracy becomes worse due to bias expansion of the mask substrate (the reticle substrate).
In order to resolve this problem, US 2009/0323039 A1 (which will later be called “Patent Literature 1”) discloses a correction method comprising: calculating thermal expansion of a photo mask (a reticle) using a model calculation; and correcting it using a high-order correction technique.
Although the correction method disclosed in Patent Literature 1 corrects the thermal expansion of the reticle using the high-order correction technique, the correction method merely corrects fluctuations of the shape of a complicated reticle due to the thermal expansion approximately using a different overlap correction technique such as a scanning rate adjustment. Therefore, the correction method disclosed in Patent Literature 1 cannot perfectly correct the thermal expansion of the reticle (residues persist).
In addition, temperature control technology of a photo mask (a reticle) is disclosed in article which is contributed by J. Mulkens et al. to Proc. of SPIE Vol. 8326 (2012), pages 12-14, and which has a title of “Driving Imaging and Overlay Performance to the Limits with Advanced Lithography Optimization” (which will later be called “Non Patent Literature 1”).
However, Non Patent Literature 1 merely discloses the temperature control technology of the photo mask (the reticle).
Furthermore, JP-A-2012-22036 (which corresponds to US 2012/0009510 A1 and which will later be called “Patent Literature 2”) discloses a lithography mask. The lithography mask disclosed in Patent Literature 2 is composed of a transparent substrate and a light blocking film or a dark film. The light blocking film (the dark film) includes a first patterning region and a second patterning region located adjacent to the first patterning region. The first patterning region corresponds to a sizable unpatterned region of a resist film, whereas the second patterning region corresponds to a patterned region of the resist film.
In the lithography mask disclosed in Patent Literature 2, if the first patterning region is adjacent to the second patterning region, the second patterning region in proximity to the first patterning region become over-exposure locally due to diffraction of the light. It therefore causes problem so that dimensional accuracy of a transferred pattern becomes worse.
Although a technique for suppressing the thermal expansion of the photo mask (the reticle) is fundamentally required, any proposal of such a technique does not be made conventionally.